Lubricating oils have been used in the past to lubricate the bearings of positive displacement compressors, to seal the rotors, and to cool the compressed gases. Lubricating oils typically used in the industry comprise a mineral oil or synthetic oil as a base oil along with various additives for a particular purpose. Thermal and oxidative stability and varnish and deposit control are some of the important properties desirable in a lubricant for maximizing the life of the lubricant, and hence, the life of the equipment, especially under the high temperature and pressure conditions created when operating a positive displacement compressor, such as a reciprocating rotary vane, scroll, or rotary screw compressor.
It has also been desirable in the industry to provide a lubricating composition that does not deteriorate due to exposure to moisture, exposure to high temperatures or use for an extended period of time. Hydrocarbon oils have very good resistance to reactions with moisture. Polyol esters have good high temperature resistance, but lesser stability to reactions with water.
U.S. Pat. No. 4,046,533 teaches branched chain alkylbenzenes can be used as lubricants for refrigerants comprising halo-substituted hydrocarbons of 1 to 3 carbon atoms and at least 40% by weight fluorine. In column 2, line 30, through column 3 line 50 it details how to identify alkylbenzenes with high amounts of branching in the alkyl group and how to identify the halo-substituted hydrocarbons. The examples of the halo-substituted hydrocarbons all contain chlorine atoms.
U.S. Pat. No. 4,302,343 describes esters of hindered polyhydric alcohols having 3 to 8 hydroxyl groups and 5 to 10 carbon atoms with one or more alkanoic acids having 4 to 18 carbon atoms. The lubricant of this patent is a blend of these esters with polyether polyols. The lubricant is used for rotary screw compressors.
U.S. Pat. No. 4,755,316 describes polyalkylene glycol lubricants to be used with a new refrigerant R-134 (tetrafluoroethane) developed to minimize concerns over ozone depletion by the halo-fluorocarbons. The patent discusses that mineral oil, a conventional lubricant with R-12 is not miscible with R134a and thus a search was made for lubricating oils meeting all of the requirements of compression refrigeration along with miscibility with R134a.
EPO 422 185B published to the Lubrizol Corporation for the use of polyol esters with hydrofluorocarbon lubricants such as R134a. The preferred polyol esters in this application were those soluble with hydrofluorocarbon lubricants over the operational range of the working fluids in a compression refrigeration system. This application outlined how to select different polyol esters to obtain miscibility with R134a and other properties.
U.S. Pat. No. 5,342,533 describes refrigerator oil compositions for compressors that include hydrofluorocarbons and the carboxylates of polyhydric alcohols described in U.S. Pat. No. 4,302,343 and EPO 422 185B. U.S. Pat. No. 5,342,533 also included a phosphate or phosphite in the lubricants and optionally included small amounts of mineral oil and/or alkylbenzene.
U.S. Pat. Nos. 6,207,071 and 6,252,300 relate to alkylbenzenes of 200 to 350 molecular weight used in compression refrigeration systems with R134a and/or R125. The application shows that lubricant compositions predominantly of alkylbenzenes cause seizure of the compressor parts after extended use if the molecular weight of 60% of the alkylbenzenes does not fall within these ranges. A phosphorus compound is optionally included in the lubricant.